In September 2016, the US government presented a report about the potential of US offshore wind energy, using wind data at 100 m altitude. Assumed confinement: within 200 nautical miles from shore. Total theoretical potential: 10,800 GW or 44,000 TWh per year. But this potential is not going to be realized. To come to a more realistic assessment, all ocean water depths over 1000 m were ignored as well as depths over 60 m in the Great Lakes (because of ice). Next areas with lower average wind speed were eliminated. Applying these restrictions the study arrived at a offshore wind energy potential of more than 2,000 GW or 7,200 TWh per year. Which is still double the current US electricity consumption.
The colored areas are potential offshore wind turbine installation areas.
It needs to be remarked that apparently most of the offshore wind energy potential will have to be realized with floating wind turbines, a technology not much applied yet. Compare these 2,000 GW with the 1,600 GW potential for the North Sea alone, that can be completely realized with monopile structures.